Pumping cassette

ABSTRACT

A pumping cassette including a housing having at least two inlet fluid lines and at least two outlet fluid lines. At least one balancing pod within the housing and in fluid connection with the fluid paths. The balancing pod balances the flow of a first fluid and the flow of a second fluid such that the volume of the first fluid equals the volume of the second fluid. The balancing pod also includes a membrane that forms two balancing chambers. Also included in the cassette is at least two reciprocating pressure displacement membrane pumps. The pumps are within the housing and they pump the fluid from a fluid inlet to a fluid outlet line and pump the second fluid from a fluid inlet to a fluid outlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/589,829, filed on Jan. 5, 2015 and issued on Jul. 11, 2017 as U.S.Pat. No. 9,700,660, which is a continuation of U.S. patent applicationSer. No. 13/684,995, filed on Nov. 26, 2012 and issued on Jan. 6, 2015as U.S. Pat. No. 8,926,294, which is a continuation of U.S. patentapplication Ser. No. 11/871,712, filed on Oct. 12, 2007 and issued onNov. 27, 2012 as U.S. Pat. No. 8,317,492, which claims priority from thefollowing U.S. Provisional Patent Applications:

U.S. Provisional Patent Application No. 60/904,024 entitled HemodialysisSystem and Methods filed on Feb. 27, 2007; and

U.S. Provisional Patent Application No. 60/921,314 entitled SensorApparatus filed on Apr. 2, 2007. Each of the three above-indicatedpriority applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to a cassette for pumping fluid.

SUMMARY OF THE INVENTION

In accordance with one aspect of the pumping cassette, the cassette is acassette including a housing having at least two inlet fluid lines andat least two outlet fluid lines. At least one balancing pod within thehousing and in fluid connection with the fluid paths. The balancing podbalances the flow of a first fluid and the flow of a second fluid suchthat the volume of the first fluid equals the volume of the secondfluid. The balancing pod also includes a membrane that forms twobalancing chambers. Also included in the cassette is at least tworeciprocating pressure displacement membrane pumps. The pumps are withinthe housing and they pump the fluid from a fluid inlet to a fluid outletline and pump the second fluid from a fluid inlet to a fluid outlet.

Various embodiments of this aspect of the cassette include one or moreof the following. Where the reciprocating pressure displacement pumpsincludes a curved rigid chamber wall and a flexible membrane attached tothe rigid chamber wall. The flexible membrane and the rigid chamber walldefine a pumping chamber. Also, where the cassette housing includes atop plate, midplate and a bottom plate. Also, where the cassette furtherincludes a metering pump within the housing. The metering pump isfluidly connected to a fluid line and pumps a volume of a fluid. Also,where the pressure pump and the metering pump are pneumatically actuatedpumps. Also, where the metering pump pumps a volume of a fluid such thatthe fluid bypasses the balancing chambers and the metering pump is amembrane pump. Also, where the cassette includes at least one fluidvalve. Also, where the cassette includes at least two fluid valvesactuated by one pneumatic valve.

In accordance with another aspect of the cassette is a cassetteincluding a housing that includes at least one inlet fluid line and atleast one outlet fluid line. The cassette also includes at least onebalancing pod within the housing and in fluid connection with the fluidpaths. The balancing pod balances the flow of a first fluid and the flowof a second fluid such that the volume of the first fluid equals thevolume of the second fluid. The balancing pod includes a membranewherein the membrane forms two chambers within the balancing pod. Alsoincluded in the cassette is at least one reciprocating pressuredisplacement membrane pump within the housing. The pressure pump pumps afluid from the fluid inlet line to the fluid outlet line. A meteringpump is also included within the housing. The metering pump is fluidlyconnected to a fluid line. The metering pump pumps a predeterminedvolume of a fluid such that the fluid bypasses the balancing chambersand wherein the metering pump is a membrane pump.

Various embodiments of this aspect of the cassette include one or moreof the following. Where the reciprocating pressure displacement pumpsincludes a curved rigid chamber wall and a flexible membrane attached tothe rigid chamber wall. The flexible membrane and the rigid chamber walldefine a pumping chamber. Also, where the cassette housing includes atop plate, a midplate and a bottom plate. Also, where the cassettefurther includes a at least one fluid valve, and/or where the fluidvalve is actuated by one pneumatic valve. Also, where the cassetteincludes at least two fluid valves actuated by one pneumatic valve.

In accordance with another aspect of the pumping cassette, the pumpingcassette includes a housing that includes at least two inlet fluid linesand at least two outlet fluid lines. Also, at least two balancing podswithin the housing and in fluid connection with the fluid lines. Thebalancing pods balance the flow of pure dialysate and impure dialysatesuch that the volume of pure dialysate equals the volume of impuredialysate. At least two reciprocating pressure displacement membranepumps are also included in the housing. The pressure pumps pump the puredialysate and said impure dialysate. A UF metering pump is also includedwithin the housing. The UF metering pump pumps a predetermined volume ofimpure dialysate from the at least one fluid line such that thepredetermined volume bypasses said balancing chamber.

Various embodiments of this aspect of the cassette include one or moreof the following. Where the reciprocating pressure displacement pumpsincludes a curved rigid chamber wall and a flexible membrane attached tothe rigid chamber wall. The flexible membrane and the rigid chamber walldefine a pumping chamber. Also, where the cassette housing includes atop plate, a midplate and a bottom plate. Also, a plurality ofpneumatically actuated fluid valves.

These aspects of the invention are not meant to be exclusive and otherfeatures, aspects, and advantages of the present invention will bereadily apparent to those of ordinary skill in the art when read inconjunction with the appended claims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings wherein:

FIG. 1A is a sectional view of one embodiment of a pod pump that isincorporated into embodiments of the cassette;

FIG. 1B is a sectional view of an exemplary embodiment of a pod pumpthat is incorporated into embodiments of the cassette;

FIG. 2A is an illustrative sectional view of one embodiment of one typeof pneumatically controlled valve that is incorporated into someembodiments of the cassette;

FIG. 2B is a sectional view of another embodiment of one type ofpneumatically controlled valve that is incorporated into someembodiments of the cassette;

FIG. 2C is a sectional view of another embodiment of one type ofpneumatically controlled valve that is incorporated into someembodiments of the cassette;

FIG. 2D is a sectional view of another embodiment of one type ofpneumatically controlled valve that is incorporated into someembodiments of the cassette;

FIGS. 2E-2F are top and bottom views of embodiments of the valvingmembrane;

FIG. 2G shows pictorial, top and cross sectional views of one embodimentof the valving membrane;

FIG. 3 is a section view of a pod pump within a cassette;

FIG. 4 is a section view of a pod pump within a cassette having avariable membrane;

FIGS. 4A and 4B are top and section views respectively of adimpled/variable membrane;

FIGS. 4C and 4D are pictorial views of a single ring membrane with avariable surface;

FIGS. 5A-5D are pictorial views of various embodiments of variablemembranes;

FIGS. 5E-5H are pictorial views of various embodiments of the meteringpump membrane;

FIGS. 6A and 6B are pictorial views of a double ring membrane with asmooth surface;

FIGS. 6C and 6D are pictorial views of a double ring membrane with adimple surface;

FIGS. 6E and 6F are pictorial views of double ring membranes withvariable surfaces;

FIG. 6G is a cross sectional view of a double ring membrane with avariable surface;

FIG. 7 is a schematic showing a pressure actuation system that may beused to actuate a pod pump;

FIG. 8A is one embodiment of the fluid flow-path schematic of thecassette;

FIG. 8B is an alternate embodiment of the fluid flow-path schematic ofthe cassette;

FIG. 9A is an isometric bottom view of the exemplary embodiment of themidplate of the exemplary embodiment of the cassette;

FIG. 9B is an isometric top view of the of the midplate of the exemplaryembodiment of the cassette;

FIG. 9C is an isometric bottom view of the exemplary embodiment of themidplate of the cassette;

FIG. 9D is a side view of the exemplary embodiment of the midplate ofthe cassette;

FIGS. 10A-10B are isometric and top views of the exemplary embodiment ofthe top plate of the exemplary embodiment of the cassette;

FIGS. 10C-10D are isometric views of the of the exemplary embodiment ofthe top plate of the exemplary embodiment of the cassette;

FIG. 10E is a side view of the exemplary embodiment of the top plate ofthe cassette;

FIGS. 11A and 11B are isometric bottom views of the exemplary embodimentof bottom plate of the exemplary embodiment of the cassette;

FIGS. 11C and 11D are isometric top views of the exemplary embodiment ofthe bottom plate of the exemplary embodiment of the cassette;

FIG. 11E is a side view of the exemplary embodiment of the bottom plateof the exemplary embodiment of the cassette;

FIG. 12A is an isometric view of the top of the assembled exemplaryembodiment of the cassette;

FIG. 12B is an isometric view of the bottom of the assembled exemplaryembodiment of the cassette;

FIG. 12C is an exploded view of the assembled exemplary embodiment ofthe cassette;

FIG. 12D is an exploded view of the assembled exemplary embodiment ofthe cassette;

FIGS. 13A-13C show cross sectional views of the exemplary embodiment ofthe assembled cassette;

FIGS. 14A-14B show isometric and top views of an alternate embodiment ofthe top plate according to an alternate embodiment of the cassette;

FIGS. 14C-14D show isometric and bottom views of an alternate embodimentof the top plate according to an alternate embodiment of the cassette;

FIG. 14E shows a side view of the alternate embodiment of the top plate;

FIGS. 15A-15B show isometric and top views of an alternate embodiment ofthe midplate according to an alternate embodiment of the cassette;

FIGS. 15C-15D show isometric and bottom views of an alternate embodimentof the midplate according to an alternate embodiment of the cassette;

FIG. 15E shows a side view of the alternate embodiment of the midplate;

FIGS. 16A-16B show isometric and top views of an alternate embodiment ofthe bottom plate according to an alternate embodiment of the cassette;

FIGS. 16C-16D show isometric and bottom views of an alternate embodimentof the bottom plate according to an alternate embodiment of thecassette;

FIG. 16E shows a side view of the alternate embodiment of the bottomplate;

FIG. 17A is an isometric top view of an assembled alternate embodimentof the cassette;

FIG. 17B is an isometric bottom view of an assembled alternateembodiment of the cassette;

FIG. 17C is an exploded view of the assembled alternate embodiment ofthe cassette;

FIG. 17D is an exploded view of the assembled alternate embodiment ofthe cassette;

FIG. 17E shows a cross sectional view of the exemplary embodiment of theassembled cassette;

FIGS. 18A-18B show isometric and top views of an alternate embodiment ofthe top plate according to an alternate embodiment of the cassette;

FIGS. 18C-18D show isometric and bottom views of an alternate embodimentof the top plate according to an alternate embodiment of the cassette;

FIG. 18E shows a side view of the alternate embodiment of the top plate;

FIGS. 19A-19B show isometric and top views of an alternate embodiment ofthe midplate according to an alternate embodiment of the cassette;

FIGS. 19C-19D show isometric and bottom views of an alternate embodimentof the midplate according to an alternate embodiment of the cassette;

FIG. 19E shows a side view of the alternate embodiment of the midplate;

FIGS. 20A-20B show isometric and top views of an alternate embodiment ofthe bottom plate according to an alternate embodiment of the cassette;

FIGS. 20C-20D show isometric and bottom views of an alternate embodimentof the bottom plate according to an alternate embodiment of thecassette;

FIG. 20E shows a side view of the alternate embodiment of the bottomplate;

FIG. 21A is a top view of an assembled alternate embodiment of thecassette;

FIG. 21B is a bottom view of an assembled alternate embodiment of thecassette;

FIG. 21C is an exploded view of the assembled alternate embodiment ofthe cassette;

FIG. 21D is an exploded view of the assembled alternate embodiment ofthe cassette;

FIG. 22A shows a cross sectional view of the exemplary embodiment of theassembled cassette; and

FIG. 22B shows a cross sectional view of the exemplary embodiment of theassembled cassette.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 1. Pumping Cassette

1.1 Cassette

The pumping cassette include various features, namely, pod pumps, fluidlines and in some embodiment, valves. The cassette embodiments shown anddescribed in this description include exemplary and some alternateembodiments. However, any variety of cassettes having a similarfunctionality is contemplated.

As well, although the cassette embodiments described herein areimplementations of the fluid schematics as shown in FIGS. 8A and 8B, inother embodiments, the cassette may have varying fluid paths and/orvalve placement and/or pod pump placements and numbers and thus, isstill within the scope of the invention.

In the exemplary embodiment, the cassette includes a top plate, amidplate and a bottom plate. There are a variety of embodiments for eachplate. In general, the top plate includes pump chambers and fluid lines,the midplate includes complementary fluid lines, metering pumps andvalves and the bottom plate includes actuation chambers (and in someembodiments, the top plate and the bottom plate include complementaryportions of a balancing chamber).

In general, the membranes are located between the midplate and thebottom plate. However, with respect to balancing chambers, a portion ofa membrane is located between the midplate and the top plate. Someembodiments include where the membrane is attached to the cassette,either overmolded, captured, bonded, press fit, welded in or any otherprocess or method for attachment. However, in the exemplary embodiments,the membranes are separate from the top plate, midplate and bottom plateuntil the plates are assembled.

The cassettes may be constructed of a variety of materials. Generally,in the various embodiments, the materials used are solid and nonflexible. In the preferred embodiment, the plates are constructed ofpolysulfone, but in other embodiments, the cassettes are constructed ofany other solid material, and in exemplary embodiments, of anythermoplastic or thermosot. In some embodiments the cassettes areconstructed of polycarbonate.

In the exemplary embodiment, the cassettes are formed by placing themembranes in their correct locations, assembling the plates in order,and connecting the plates. In one embodiment, the plates are connectedusing a laser welding technique. However, in other embodiments, theplates may be glued, mechanically fastened, strapped together,ultrasonically welded, or any other mode of attaching the platestogether.

In practice, the cassette may be used to pump any type of fluid from anysource to any location. The types of fluid include nutritive,nonnutritive, inorganic chemicals, organic chemicals, bodily fluids orany other type of fluid. Additionally, fluid in some embodiments includea gas. Thus, in some embodiments, the cassette is used to pump a gas.

The cassette serves to pump and direct the fluid from and to the desiredlocations. In some embodiments, outside pumps pump the fluid into thecassette and the cassette pumps the fluid out. However, in someembodiments, the pod pumps serve to pull the fluid into the cassette andpump the fluid out of the cassette.

As discussed above, depending on the valve locations, control of thefluid paths is imparted. Thus, the valves being in different locationsor additional valves are alternate embodiments of this cassette.Additionally, the fluid lines and paths shown in the figures describedabove are mere examples of fluid lines and paths. Other embodiments mayhave more, less and/or different fluid paths. In still otherembodiments, valves are not present in the cassette.

The number of pod pumps described above may also vary depending on theembodiment. For example, although the exemplary and alternateembodiments shown and described above include two pod pumps, in otherembodiments, the cassette includes one. In still other embodiments, thecassette includes more than two pod pumps. The pod pumps can be singlepumps or work in tandem to provide a more continuous flow. Either orboth may be used in various embodiments of the cassette.

The various fluid inlets and fluid outlets are fluid ports. In practice,depending on the valve arrangement and control, a fluid inlet can be afluid outlet. Thus, the designation of the fluid port as a fluid inletor a fluid outlet is only for description purposes. The variousembodiments have interchangeable fluid ports. The fluid ports areprovided to impart particular fluid paths onto the cassette. These fluidports are not necessarily all used all of the time; instead, the varietyof fluid ports provides flexibility of use of the cassette in practice.

1.2 Exemplary Pressure Pod Pump Embodiments

FIG. 1A is a sectional view of an exemplary pod pump 100 that isincorporated into a fluid control or pump cassette (see also FIGS. 3 and4), in accordance with an exemplary embodiment of the cassette. In thisembodiment, the pod pump is formed from three rigid pieces, namely a“top” plate 106, a midplate 108, and a “bottom” plate 110 (it should benoted that the terms “top” and “bottom” are relative and are used herefor convenience with reference to the orientation shown in FIG. 1A). Thetop and bottom plates 106 and 110 include generally hemispheroidportions that when assembled together define a hemispheroid chamber,which is a pod pump 100.

A membrane 112 separates the central cavity of the pod pump into twochambers. In one embodiment, these chambers are: the pumping chamberthat receives the fluid to be pumped, and an actuation chamber forreceiving the control gas that pneumatically actuates the pump. An inlet102 allows fluid to enter the pumping chamber, and an outlet 104 allowsfluid to exit the pumping chamber. The inlet 102 and the outlet 104 maybe formed between midplate 108 and the top plate 106. Pneumatic pressureis provided through a pneumatic port 114 to either force, with positivegas pressure, the membrane 112 against one wall of pod pump cavity tominimize the pumping chamber's volume, or to draw, with negative gaspressure, the membrane 112 towards the other wall of the pod pump 100cavity to maximize the pumping chamber's volume.

The membrane 112 is provided with a thickened rim 116, which is heldtightly by a protrusion 118 in the midplate 108. Thus, in manufacture,the membrane 112 can be placed in and held by the groove 108 before thebottom plate 110 is connected (in the exemplary embodiment) to themidplate 108.

Although not shown in FIGS. 1A and 1B, in some embodiments of the podpump, on the fluid side, a groove is present on the chamber wall. Thegroove acts to prevent folds in the membrane from trapping fluid in thechamber when emptying.

Referring first to FIG. 1A, a cross sectional view of a reciprocatingpositive-displacement pump 100 in a cassette is shown. The pod pump 100includes a flexible membrane 112 (also referred to as the “pumpdiaphragm” or “membrane”) mounted where the pumping chamber (alsoreferred to as a “liquid chamber” or “liquid pumping chamber”) wall 122and the actuation chamber (also referred to as the “pneumatic chamber”)wall 120 meet. The membrane 112 effectively divides that interior cavityinto a variable-volume pumping chamber (defined by the rigid interiorsurface of the pumping chamber wall 122 and a surface of the membrane112) and a complementary variable-volume actuation chamber (defined bythe rigid interior surface of the actuation chamber wall 120 and asurface of the membrane 112). The top portion 106 includes a fluid inlet102 and a fluid outlet 104, both of which are in fluid communicationwith the pumping/liquid chamber. The bottom portion 110 includes anactuation or pneumatic interface 114 in fluid communication with theactuation chamber. As discussed in greater detail below, the membrane112 can be urged to move back and forth within the cavity by alternatelyapplying negative or vent to atmosphere and positive pneumatic pressureat the pneumatic interface 114. As the membrane 112 reciprocates backand forth, the sum of the volumes of the pumping and actuation chambersremains constant.

During typical fluid pumping operations, the application of negative orvent to atmosphere pneumatic pressure to the actuation or pneumaticinterface 114 tends to withdraw the membrane 112 toward the actuationchamber wall 120 so as to expand the pumping/liquid chamber and drawfluid into the pumping chamber through the inlet 102, while theapplication of positive pneumatic pressure tends to push the membrane112 toward the pumping chamber wall 122 so as to collapse the pumpingchamber and expel fluid in the pumping chamber through the outlet 104.During such pumping operations, the interior surfaces of the pumpingchamber wall 122 and the actuation chamber wall 120 limit movement ofthe membrane 112 as it reciprocates back and forth. In the embodimentshown in FIG. 1A, the interior surfaces of the pumping chamber wall 122and the actuation chamber wall 120 are rigid, smooth, and hemispherical.In lieu of a rigid actuation chamber wall 120, an alternative rigidlimit structure—for example, a portion of a bezel used for providingpneumatic pressure and/or a set of ribs—may be used to limit themovement of the membrane as the pumping chamber approaches maximumvalue. Bezels and rib structures are described generally in U.S. patentapplication Ser. No. 10/697,450 entitled BEZEL ASSEMBLY FOR PNEUMATICCONTROL filed on Oct. 30, 2003 and published as Publication No. US2005/0095154 and related PCT Application No. PCT/US2004/035952 entitledBEZEL ASSEMBLY FOR PNEUMATIC CONTROL filed on Oct. 29, 2004 andpublished as Publication No. WO 2005/044435, both of which are herebyincorporated herein by reference in their entireties. Thus, the rigidlimit structure—such as the rigid actuation chamber wall 120, a bezel,or a set of ribs—defines the shape of the membrane 112 when the pumpingchamber is at its maximum value. In a preferred embodiment, the membrane112 (when urged against the rigid limit structure) and the rigidinterior surface of the pumping chamber wall 122 define a sphericalpumping chamber volume when the pumping chamber volume is at a minimum.

Thus, in the embodiment shown in FIG. 1A, movement of the membrane 112is limited by the pumping chamber wall 122 and the actuation chamberwall 120. As long as the positive and vent to atmosphere or negativepressurizations provided through the pneumatic port 114 are strongenough, the membrane 112 will move from a position limited by theactuation chamber wall 120 to a position limited by the pumping chamberwall 122. When the membrane 112 is forced against the actuation chamberwall 120, the membrane and the pumping chamber wall 122 define themaximum volume of the pumping chamber. When the membrane is forcedagainst the pumping chamber wall 122, the pumping chamber is at itsminimum volume.

In an exemplary embodiment, the pumping chamber wall 122 and theactuation chamber wall 120 both have a hemispheroid shape so that thepumping chamber will have a spheroid shape when it is at its maximumvolume. By using a pumping chamber that attains a spheroid shape—andparticularly a spherical shape—at maximum volume, circulating flow maybe attained throughout the pumping chamber. Such shapes accordingly tendto avoid stagnant pockets of fluid in the pumping chamber. As discussedfurther below, the orientations of the inlet 102 and outlet 104 alsotend to have an impact on the flow of fluid through the pumping chamberand in some embodiments, reduce the likelihood of stagnant pockets offluid forming. Additionally, compared to other volumetric shapes, thespherical shape (and spheroid shapes in general) tends to create lessshear and turbulence as the fluid circulates into, through, and out ofthe pumping chamber.

Referring now to FIGS. 3-4, a raised flow path 30 is shown in thepumping chamber. This raised flow path 30 allows for the fluid tocontinue flowing through the pod pumps after the membrane reaches theend of stroke. Thus, the raised flow path 30 minimizes the chances ofthe membrane causing air or fluid to be trapped in the pod pump or themembrane blocking the inlet or outlet of the pod pump which wouldinhibit continuous flow. The raised flow path 30 is shown in theexemplary embodiment having particular dimensions. However, in alternateembodiments, as seen in FIGS. 18A-18E, the raised flow path 30 isnarrower, or in still other embodiments, the raised flow path 30 can beany dimensions as the purpose is to control fluid flow so as to achievea desired flow rate or behavior of the fluid. Thus, the dimensions shownand described here with respect to the raised flow path, the pod pumps,the valves, or any other aspect are mere exemplary and alternateembodiments. Other embodiments are readily apparent.

1.3 Exemplary Balancing Pods Embodiment

Referring now to FIG. 1B, an exemplary embodiment of a balancing pod isshown. The balancing pod is constructed similar to the pod pumpdescribed above with respect to FIG. 1A. However, a balancing podincludes two fluid balancing chambers, rather than an actuation chamberand a pumping chamber, and does not include an actuation port.Additionally, each balancing chamber includes an inlet 102 and an outlet104. In the exemplary embodiment, a groove 126 is included on each ofthe balancing chamber walls 120, 122. The groove 126 is described infurther detail below.

The membrane 112 provides a seal between the two chambers. The balancingchambers work to balance the flow of fluid into and out of the chamberssuch that both chambers maintain an equal volume rate flow. Although theinlets 102 and outlets 104 for each chamber are shown to be on the sameside, in other embodiments, the inlets 102 and outlets 104 for eachchamber are on different sides. Also, the inlets 102 and outlets 104 canbe on either side, depending on the flow path in which the balancingchamber is integrated.

In one embodiment of the balancing chambers the membrane 112 includes anembodiment similar to the one described below with respect to FIG.6A-6G. However, in alternate embodiments, the membrane 112 can be overmolded or otherwise constructed such that a double-ring seal is notapplicable.

1.4 Metering Pumps and Fluid Management System

The metering pump can be any pump that is capable of adding any fluid orremoving any fluid. The fluids include but are not limited topharmaceuticals, inorganic compounds or elements, organic compounds orelements, nutraceuticals, nutritional elements or compounds orsolutions, or any other fluid capable of being pumped. In oneembodiment, the metering pump is a membrane pump. In the exemplaryembodiment, the metering pump is a smaller volume pod pump. In theexemplary embodiment, the metering pump includes an inlet and an outlet,similar to a larger pod pump (as shown in FIG. 1A for example). However,the inlet and outlet are generally much smaller than a pod pump and, inone exemplary embodiment, includes a volcano valve-like raised ringaround either the inlet or outlet. Metering pumps include a membrane,and various embodiments of a metering pump membrane are shown in FIGS.5E-5H. The metering pump, in some embodiments, pumps a volume of fluidout of the fluid line. Once the fluid is in the pod pump, a referencechamber, located outside the cassette, using the FMS, determines thevolume that has been removed.

Thus, depending on the embodiment, this volume of fluid that has beenremoved will not then flow to the fluid outlet, the balance chambers orto a pod pump. Thus, in some embodiments, the metering pump is used toremove a volume of fluid from a fluid line. In other embodiments, themetering pump is used to remove a volume of fluid to produce otherresults.

FMS may be used to perform certain fluid management system measurements,such as, for example, measuring the volume of subject fluid pumpedthrough the pump chamber during a stroke of the membrane or detectingair in the pumping chamber, e.g., using techniques described in U.S.Pat. Nos. 4,808,161; 4,826,482; 4,976,162; 5,088,515; and 5,350,357,which are hereby incorporated herein by reference in their entireties.

Metering pumps are also used in various embodiments to pump a secondfluid into the fluid line. In some embodiments, the metering pump isused to pump a therapeutic or a compound into a fluid line. Oneembodiment uses the metering pump to pump a volume of compound into amixing chamber in order to constitute a solution. In some of theseembodiments, the metering pumps are configured for FMS volumemeasurement. In other embodiments, the metering pumps are not.

For FMS measurement, a small fixed reference air chamber is locatedoutside of the cassette, for example, in the pneumatic manifold (notshown). A valve isolates the reference chamber and a second pressuresensor. The stroke volume of the metering pump may be precisely computedby charging the reference chamber with air, measuring the pressure, andthen opening the valve to the pumping chamber. The volume of air on thechamber side may be computed based on the fixed volume of the referencechamber and the change in pressure when the reference chamber wasconnected to the pump chamber.

1.5 Valves

The exemplary embodiment of the cassette includes one or more valves.Valves are used to regulate flow by opening and closing fluid lines. Thevalves included in the various embodiments of the cassette include oneor more of the following: volcano valves or smooth valves. In someembodiments of the cassette, check valves may be included. Embodimentsof the volcano valve are shown in FIGS. 2A and 2B, while an embodimentof the smooth valve is shown in FIG. 2C. Additionally, FIGS. 3 and 4show cross sections of one embodiment of a pod pump in a cassette withan inlet and an outlet valve.

Generally speaking, reciprocating positive-displacement pumps of thetypes just described may include, or may be used in conjunction with,various valves to control fluid flow through the pump. Thus, forexample, the reciprocating positive-displacement pump or the balancingpods may include, or be used in conjunction with, an inlet valve and/oran outlet valve. The valves may be passive or active. In the exemplaryembodiment of the reciprocating positive-displacement pump the membraneis urged back and forth by positive and negative pressurizations, or bypositive and vent to atmosphere pressurizations, of a gas providedthrough the pneumatic port, which connects the actuation chamber to apressure actuation system. The resulting reciprocating action of themembrane pulls fluid into the pumping chamber from the inlet (the outletvalve prevents liquid from being sucked back into the pumping chamberfrom the outlet) and then pushes the fluid out of the pumping chamberthrough the outlet (the inlet valve prevents fluid from being forcedback from the inlet).

In the exemplary embodiments, active valves control the fluid flowthrough the pump(s) and the cassette. The active valves may be actuatedby a controller in such a manner as to direct flow in a desireddirection. Such an arrangement would generally permit the controller tocause flow in either direction through the pod pump. In a typicalsystem, the flow would normally be in a first direction, e.g., from theinlet to the outlet. At certain other times, the flow may be directed inthe opposite direction, e.g., from the outlet to the inlet. Suchreversal of flow may be employed, for example, during priming of thepump, to check for an aberrant line condition (e.g., a line occlusion,blockage, disconnect, or leak), or to clear an aberrant line condition(e.g., to try to dislodge a blockage).

Pneumatic actuation of valves provides pressure control and a naturallimit to the maximum pressure that may be developed in a system. In thecontext of a system, pneumatic actuation has the added benefit ofproviding the opportunity to locate all the solenoid control valves onone side of the system away from the fluid paths.

Referring now to FIGS. 2A and 2B, sectional views of two embodiments ofa volcano valve are shown. The volcano valves are pneumaticallycontrolled valves that may be used in embodiments of the cassette. Amembrane 202, along with the midplate 204, defines a valving chamber206. Pneumatic pressure is provided through a pneumatic port 208 toeither force, with positive gas pressure, the membrane 202 against avalve seat 210 to close the valve, or to draw, with negative gaspressure, or in some embodiments, with vent to atmospheric pressure, themembrane away from the valve seat 210 to open the valve. A control gaschamber 212 is defined by the membrane 202, the top plate 214, and themidplate 204. The midplate 204 has an indentation formed on it, intowhich the membrane 202 is placed so as to form the control gas chamber212 on one side of the membrane 202 and the valving chamber 206 on theother side.

The pneumatic port 208 is defined by a channel formed in the top plate214. By providing pneumatic control of several valves in a cassette,valves can be ganged together so that all the valves ganged together canbe opened or closed at the same time by a single source of pneumaticpressure. Channels formed on the midplate 204, corresponding with fluidpaths along with the bottom plate 216, define the valve inlet 218 andthe valve outlet 220. Holes formed through the midplate 204 providecommunication between the inlet 218 and the valving chamber 206 andbetween the valving chamber 206 and the outlet 220.

The membrane 202 is provided with a thickened rim 222, which fitstightly in a groove 224 in the midplate 204. Thus, the membrane 202 canbe placed in and held by the groove 224 before the top plate 214 isconnected to the midplate 204. Thus, this valve design may impartbenefits in manufacture. As shown in FIGS. 2B and 2C, the top plate 214may include additional material extending into control gas chamber 212so as to prevent the membrane 202 from being urged too much in adirection away from the groove 224, so as to prevent the membrane'sthickened rim 222 from popping out of the groove 224. The location ofthe pneumatic port 208 with respect to the control gas chamber 212varies in the two embodiments shown in FIGS. 2A and 2B.

FIG. 2C shows an embodiment in which the valving chamber lacks a valveseat feature. Rather, in FIG. 2C, the valve in this embodiment does notinclude any volcano features and thus, the valving chamber 206, i.e.,the fluid side, does not include any raised features and thus is smooth.This embodiment is used in cassettes used to pump fluid sensitive toshearing. FIG. 2D shows an embodiment in which the valving chamber has araised area to aid in the sealing of the valving membrane. Referring nowto FIGS. 2E-2G, various embodiments of the valve membrane are shown.Although some exemplary embodiments have been shown and described, inother embodiments, variations of the valve and valving membrane may beused.

1.6 Exemplary Embodiments of the Pod Membrane

In some embodiments, the membrane has a variable cross-sectionalthickness, as shown in FIG. 4. Thinner, thicker or variable thicknessmembranes may be used to accommodate the strength, flexural and otherproperties of the chosen membrane's materials. Thinner, thicker orvariable membrane wall thickness may also be used to manage the membranethereby encouraging it to flex more easily in some areas than in otherareas, thereby aiding in the management of pumping action and flow ofsubject fluid in the pump chamber. In this embodiment, the membrane isshown having its thickest cross-sectional area closest to its center.However, in other embodiments having a membrane with a varying crosssection, the thickest and thinnest areas may be in any location on themembrane. Thus, for example, the thinner cross section may be locatednear the center and the thicker cross sections located closer to theperimeter of the membrane. Still other configurations are possible.Referring to FIGS. 5A-5D, one embodiment of a membrane is shown havingvarious surface embodiments, these include smooth (FIG. 5A), rings (FIG.5D), ribs (FIG. 5C), dimples or dots (FIG. 5B) of variable thickness andor geometry located at various locations on the actuation and or pumpingside of the membrane. In one embodiment of the membrane, the membranehas a tangential slope in at least one section, but in otherembodiments, the membrane is completely smooth or substantially smooth.

Referring now to FIGS. 4A, 4C and 4D, an alternate embodiment of themembrane is shown. In this embodiment, the membrane has a dimpled ordotted surface.

The membrane may be made of any flexible material having a desireddurability and compatibility with the subject fluid. The membrane can bemade from any material that may flex in response to fluid, liquid or gaspressure or vacuum applied to the actuation chamber. The membranematerial may also be chosen for particular bio-compatibility,temperature compatibility or compatibility with various subject fluidsthat may be pumped by the membrane or introduced to the chambers tofacilitate movement of the membrane. In the exemplary embodiment, themembrane is made from high elongation silicone. However, in otherembodiments, the membrane is made from any elastomer or rubber,including, but not limited to, silicone, urethane, nitrile, EPDM or anyother rubber, elastomer or flexible material.

The shape of the membrane is dependent on multiple variables. Thesevariables include, but are not limited to: the shape of the chamber; thesize of the chamber; the subject fluid characteristics; the volume ofsubject fluid pumped per stroke; and the means or mode of attachment ofthe membrane to the housing. The size of the membrane is dependent onmultiple variables. These variables include, but are not limited to: theshape of the chamber; the size of the chamber; the subject fluidcharacteristics; the volume of subject fluid pumped per stroke; and themeans or mode of attachment of the membrane to the housing. Thus,depending on these or other variables, the shape and size of themembrane may vary in various embodiments.

The membrane can have any thickness. However, in some embodiments, therange of thickness is between 0.002 inches to 0.125 inches. Depending onthe material used for the membrane, the desired thickness may vary. Inone embodiment, high elongation silicone is used in a thickness rangingfrom 0.015 inches to 0.050 inches. However, in other embodiments, thethickness may vary.

In the exemplary embodiment, the membrane is preformed to include asubstantially dome shape in at least part of the area of the membrane.One embodiment of the dome-shaped membrane is shown in FIGS. 4C and 4D.Again, the dimensions of the dome may vary based on some or more of thevariables described above. However, in other embodiments, the membranemay not include a preformed dome shape.

In the exemplary embodiment, the membrane dome is formed using liquidinjection molding. However, in other embodiments, the dome may be formedby using compression molding. In alternate embodiments, the membrane issubstantially flat. In other embodiments, the dome size, width, orheight may vary.

In various embodiments, the membrane may be held in place by variousmeans and methods. In one embodiment, the membrane is clamped betweenthe portions of the cassette, and in some of these embodiments, the rimof the cassette may include features to grab the membrane. In others ofthis embodiment, the membrane is clamped to the cassette using at leastone bolt or another device. In another embodiment, the membrane isover-molded with a piece of plastic and then the plastic is welded orotherwise attached to the cassette. In another embodiment, the membraneis pinched between the mid plate described with respect to FIGS. 1A and1B and the bottom plate. Although some embodiments for attachment of themembrane to the cassette are described, any method or means forattaching the membrane to the cassette can be used. The membrane, in onealternate embodiment, is attached directly to one portion of thecassette. In some embodiments, the membrane is thicker at the edge,where the membrane is pinched by the plates, than in other areas of themembrane. In some embodiments, this thicker area is a gasket, and insome embodiments an O-ring, ring, or any other shaped gasket. Referringagain to FIGS. 6A-6D, one embodiment of the membrane is shown with twogaskets 62, 64. In some of these embodiments, the gaskets 62, 64 providethe attachment point of the membrane to the cassette. In otherembodiments, the membrane includes more than two gaskets. Membranes withone gasket are also included in some embodiments (see FIGS. 4A-4D).

In some embodiments of the gasket, the gasket is contiguous with themembrane. However, in other embodiments, the gasket is a separate partof the membrane. In some embodiments, the gasket is made from the samematerial as the membrane. However, in other embodiments, the gasket ismade of a material different from the membrane. In some embodiments, thegasket is formed by over-molding a ring around the membrane. The gasketcan be any shape ring or seal desired so as to complement the pod pumphousing embodiment. In some embodiments, the gasket is a compressiontype gasket.

1.7 Mixing Pods

Some embodiments of the cassette include a mixing pod. A mixing podincludes a chamber for mixing. In some embodiments, the mixing pod is aflexible structure, and in some embodiments, at least a section of themixing pod is a flexible structure. The mixing pod can include a seal,such as an o-ring, or a membrane. The mixing pod can be any shapedesired. In the exemplary embodiment, the mixing pod is similar to a podpump except it does not include a membrane and does not include anactuation port. Some embodiments of this embodiment of the mixing podinclude an o-ring seal to seal the mixing pod chamber. Thus, in theexemplary embodiment, the mixing pod is a spherical hollow pod with afluid inlet and a fluid outlet. As with the pod pumps, the chamber sizecan be any size desired.

2. Pressure Pump Actuation System

FIG. 7 is a schematic showing an embodiment of a pressure actuationsystem that may be used to actuate a pod pump with both positive andnegative pressure, such as the pod pump shown in FIG. 1A. The pressureactuation system is capable of intermittently or alternately providingpositive and negative pressurizations to the gas in the actuationchamber of the pod pump. However, in some embodiments, FIG. 7 does notapply, in these embodiments, actuation of the pod pump is accomplishedby applying positive pressure and vent to atmosphere (again, not shownin FIG. 7). The pod pump—including the flexible membrane, the inlet, theoutlet, the pneumatic port, the pumping chamber, the actuation chamber,and possibly including an inlet check valve and an outlet check valve orother valves—is part of a larger disposable system. The pneumaticactuation system—including an actuation-chamber pressure transducer, apositive-supply valve, a negative-supply valve, a positive-pressure gasreservoir, a negative-pressure gas reservoir, apositive-pressure-reservoir pressure transducer, anegative-pressure-reservoir pressure transducer, as well as anelectronic controller including, in some embodiments, a user interfaceconsole (such as a touch-panel screen)—may be part of a base unit.

The positive-pressure reservoir provides to the actuation chamber thepositive pressurization of a control gas to urge the membrane towards aposition where the pumping chamber is at its minimum volume (i.e., theposition where the membrane is against the rigid pumping-chamber wall).The negative-pressure reservoir provides to the actuation chamber thenegative pressurization of the control gas to urge the membrane in theopposite direction, towards a position where the pumping chamber is atits maximum volume (i.e., the position where the membrane is against therigid actuation-chamber wall).

A valving mechanism is used to control fluid communication between eachof these reservoirs and the actuation chamber. As shown in FIG. 7, aseparate valve is used for each of the reservoirs; a positive-supplyvalve controls fluid communication between the positive-pressurereservoir and the actuation chamber, and a negative-supply valvecontrols fluid communication between the negative-pressure reservoir andthe actuation chamber. These two valves are controlled by thecontroller. Alternatively, a single three-way valve may be used in lieuof the two separate valves. The valves may be binary on-off valves orvariable-restriction valves.

The controller also receives pressure information from the threepressure transducers: an actuation-chamber pressure transducer, apositive-pressure-reservoir pressure transducer, and anegative-pressure-reservoir pressure transducer. As their names suggest,these transducers respectively measure the pressure in the actuationchamber, the positive-pressure reservoir, and the negative-pressurereservoir. The actuation-chamber-pressure transducer is located in abase unit but is in fluid communication with the actuation chamberthrough the pod pump pneumatic port. The controller monitors thepressure in the two reservoirs to ensure they are properly pressurized(either positively or negatively). In one exemplary embodiment, thepositive-pressure reservoir may be maintained at around 750 mmHg, whilethe negative-pressure reservoir may be maintained at around −450 mmHg.

Still referring to FIG. 7, a compressor-type pump or pumps (not shown)may be used to maintain the desired pressures in these reservoirs. Forexample, two independent compressors may be used to respectively servicethe reservoirs. Pressure in the reservoirs may be managed using a simplebang-bang control technique in which the compressor servicing thepositive-pressure reservoir is turned on if the pressure in thereservoir falls below a predetermined threshold and the compressorservicing the negative-pressure reservoir is turned on if the pressurein the reservoir is above a predetermined threshold. The amount ofhysteresis may be the same for both reservoirs or may be different.Tighter control of the pressure in the reservoirs can be achieved byreducing the size of the hysteresis band, although this will generallyresult in higher cycling frequencies of the compressors. If very tightcontrol of the reservoir pressures is required or otherwise desirablefor a particular application, the bang-bang control technique could bereplaced with a PID control technique and could use PWM signals on thecompressors.

The pressure provided by the positive-pressure reservoir is preferablystrong enough—under normal conditions—to urge the membrane all the wayagainst the rigid pumping-chamber wall. Similarly, the negative pressure(i.e., the vacuum) provided by the negative-pressure reservoir ispreferably strong enough—under normal conditions—to urge the membraneall the way against the actuation-chamber wall. In a further preferredembodiment, however, these positive and negative pressures provided bythe reservoirs are within safe enough limits that even with either thepositive-supply valve or the negative-supply valve open all the way, thepositive or negative pressure applied against the membrane is not sostrong as to damage the pod pump or create unsafe fluid pressures (e.g.,that may harm a patient receiving pumped blood or other fluid).

It will be appreciated that other types of actuation systems may be usedto move the membrane back and forth instead of the two-reservoirpneumatic actuation system shown in FIG. 7, although a two-reservoirpneumatic actuation system is generally preferred. For example,alternative pneumatic actuation systems may include either a singlepositive-pressure reservoir or a single negative-pressure reservoiralong with a single supply valve and a single tank pressure sensor,particularly in combination with a resilient membrane. Such pneumaticactuation systems may intermittently provide either a positive gaspressure or a negative gas pressure to the actuation chamber of the podpump. In embodiments having a single positive-pressure reservoir, thepump may be operated by intermittently providing positive gas pressureto the actuation chamber, causing the membrane to move toward thepumping chamber wall and expel the contents of the pumping chamber, andreleasing the gas pressure, causing the membrane to return to itsrelaxed position and draw fluid into the pumping chamber. In embodimentshaving a single negative-pressure reservoir, the pump may be operated byintermittently providing negative gas pressure to the actuation chamber,causing the membrane to move toward the actuation chamber wall and drawfluid into the pumping chamber, and releasing the gas pressure, causingthe membrane to return to its relaxed position and expel fluid from thepumping chamber.

3. Fluid Handling

As shown and described with respect to FIGS. 2A-2D, a fluid valve in theexemplary embodiment consists of a small chamber with a flexiblemembrane or membrane across the center dividing the chamber into a fluidhalf and a pneumatic half. The fluid valve, in the exemplary embodiment,has three entry/exit ports, two on the fluid half of the chamber and onethe pneumatic half of the chamber. The port on the pneumatic half of thechamber can supply either positive pressure or vacuum (or rather thanvacuum, in some embodiments, there is a vent to atmosphere) to thechamber. When a vacuum is applied to the pneumatic portion of thechamber, the membrane is pulled towards the pneumatic side of thechamber, clearing the fluid path and allowing fluid to flow into and outof the fluid side of the chamber. When positive pressure is applied tothe pneumatic portion of the chamber, the membrane is pushed towards thefluid side of the chamber, blocking the fluid path and preventing fluidflow. In the volcano valve embodiment (as shown in FIGS. 2A-2B) on oneof the fluid ports, that port seals off first when closing the valve andthe remainder of any fluid in the valve is expelled through the portwithout the volcano feature. Additionally, in one embodiment of thevalves, shown in FIG. 2D, the raised feature between the two portsallows for the membrane to seal the two ports from each other earlier inthe actuation stroke (i.e., before the membrane seals the portsdirectly).

Referring again to FIG. 7, pressure valves are used to operate the pumpslocated at different points in the flow path. This architecture supportspressure control by using two variable-orifice valves and a pressuresensor at each pump chamber which requires pressure control. In oneembodiment, one valve is connected to a high-pressure source and theother valve is connected to a low-pressure sink. A high-speed controlloop monitors the pressure sensor and controls the valve positions tomaintain the necessary pressure in the pump chamber.

Pressure sensors are used to monitor pressure in the pneumatic portionof the chambers themselves. By alternating between positive pressure andvacuum on the pneumatic side of the chamber, the membrane is cycled backand forth across the total chamber volume. With each cycle, fluid isdrawn through the upstream valve of the inlet fluid port when thepneumatics pull a vacuum on the pods. The fluid is then subsequentlyexpelled through the outlet port and the downstream valve when thepneumatics deliver positive pressure to the pods.

In many embodiments, pressure pumps consist of a pair of chambers. Whenthe two chambers are run 180 degrees out of phase from one another theflow is essentially continuous.

4. Volume Measurement

These flow rates in the cassette are controlled using pressure pod pumpswhich can detect end of stroke. An outer control loop determines thecorrect pressure values to deliver the required flow. Pressure pumps canrun an end-of-stroke algorithm to detect when each stroke completes.While the membrane is moving, the measured pressure in the chambertracks a desired sinusoidal pressure. When the membrane contacts achamber wall, the pressure becomes constant, no longer tracking thesinusoid. This change in the pressure signal is used to detect when thestroke has ended, i.e., the end of stroke.

The pressure pumps have a known volume. Thus, an end of stroke indicatesa known volume of fluid is in the chamber. Thus, using the end ofstroke, fluid flow may be controlled using rate equating to volume.

As described above in more detail, FMS may be used to determine thevolume of fluid pumped by the metering pumps. In some embodiments, themetering pump may pump fluid without using the FMS volume measurementsystem, however, in the exemplary embodiments, the FMS volumemeasurement system is used to calculate the exact volume of fluidpumped.

5. Exemplary Embodiment of the Pumping Cassette

Referring now to FIG. 8A, an exemplary embodiment of the fluid schematicof the balancing pumping and metering cassette 800 is shown. Otherschematics are readily discernable. The cassette 800 includes at leastone pod pump 828, 820 and at least one balancing pod 822, 812. Thecassette 800 also includes a first fluid inlet 810, where a first fluidenters the cassette. The first fluid includes a flow rate providedoutside the cassette 800. The cassette 800 also includes a first fluidoutlet 824 where the first fluid exits the cassette 800 having a flowrate provided by one of the at least one pod pumps 828. The cassette 800includes a second fluid inlet 826 where the second fluid enters thecassette 800, and a second fluid outlet 816 where the second fluid exitsthe cassette.

Balancing pods 822, 812 in the cassette 800 provide for a desiredbalance of volume of fluid pumped into and out of the cassette 800,i.e., between the first fluid and the second fluid. The balancing pods822, 812, however, may be bypassed by way of the metering pump 830. Themetering pump 830 pumps a volume of second fluid (or first fluid inother embodiments) out of the fluid line, bypassing the balancing pod822, 812. Thus, a smaller or reduced volume (i.e., a “new” volume) ofthe fluid that has been removed by the metering pump 830 will actuallyenter the balancing pod 822, 812 and thus, the metering pump 830functions to provide a “new” volume of second fluid by removing thedesired volume from the fluid path before the second fluid reaches thebalancing pod 822, 812 (or in other embodiments, removing first fluidthe desired volume from the fluid path before the second fluid reachesthe balancing pod 822, 812) resulting in less first fluid (or in otherembodiments, second fluid) being pumped for that pump cycle.

The fluid schematic of the cassette 800 shown in FIG. 8A may be embodiedinto various cassette apparatus. Thus, the embodiments of the cassette800 including the fluid schematic shown in FIG. 8A are not the onlycassette embodiments that may incorporate this or an alternateembodiment of this fluid schematic. Additionally, the types of valves,the ganging of the valves, the number of pumps and chambers may vary invarious cassette embodiments of this fluid schematic.

Referring still to FIG. 8A, a fluid flow-path schematic 800 is shown.The fluid flow-path schematic 800 is described herein corresponding tothe flow paths in one embodiment of the cassette. The exemplaryembodiment of the midplate 900 of the cassette is shown in FIG. 9A withthe valves corresponding to the fluid flow-path schematic in FIG. 8Aindicated. The valving side of the midplate 900 shown in FIG. 9Acorresponds to the fluid side shown in FIG. 9B.

Referring first to FIG. 8A with FIG. 9A, a first fluid enters thecassette at the first fluid inlet 810. The first fluid flows tobalancing pod A 812. Balancing pod A 812 is a balancing pod as describedabove. Balancing pod A 812 initially contained a first volume of secondfluid. When the first fluid flows into the balancing pod A 812, themembrane forces the second fluid out of balancing pod A 812. The secondfluid flows through the drain path 814 and out the first fluid outlet816.

At the same time, pod pump B 820 includes a volume of second fluid. Thevolume of second fluid is pumped to balancing pod B 822. Balancing pod B822 contains a volume of first fluid, and this volume of first fluid isdisplaced by the volume of second fluid. The volume of first fluid frombalancing pod B 822 flows to the second fluid outlet 824 and exits thecassette. A volume of a second fluid enters the cassette at fluid inlettwo 826 and flows to pod pump A 828.

Referring still to FIG. 8A with FIG. 9A, the second fluid is pumped frompod pump A 828 to balancing pod A 812. The second fluid displaces thefirst fluid in balancing pod A 812. The first fluid from balancing pod A812 flows to the second fluid outlet 824.

First fluid flows into the cassette through the first fluid inlet 810and flows to balancing pod B 822. The first fluid displaces the secondfluid in balancing pod B 822, forcing the second fluid to flow out ofthe cassette through the first fluid outlet 816. Second fluid flows intothe cassette through the second fluid inlet 826 and to pod pump B 820.

The metering pump can be actuated at any time and its function is toremove fluid from the fluid path in order to bypass the balancing pod.Thus, any volume of fluid removed would act to decrease the volume ofthe other fluid flowing out of the second fluid outlet 824. The meteringpump is independent of the balancing pods 812, 822 and the pod pumps820, 828. The fluid enters through fluid inlet two 826 and is pulled bythe metering pump 830. The metering pump then pumps the volume of fluidthrough the second fluid outlet 816.

Although in the embodiment of the fluid schematic shown in FIG. 8A, themetering pump is described only with respect to second fluid enteringthe cassette through fluid inlet two 826, the metering pump can easilybypass first fluid entering the cassette through fluid inlet one 810.Thus, depending on whether the desired end result is to have less of thefirst fluid or less of the second fluid, the metering pump and valvesthat control the fluid lines in the cassette can perform accordingly toaccomplish the result.

In the exemplary fluid flow-path embodiment shown in FIG. 8A, andcorresponding structure of the cassette shown in FIG. 9A, valves areganged such that they are actuated at the same time. In the preferredembodiment, there are four gangs of valves 832, 834, 836, 838. In thepreferred embodiment, the ganged valves are actuated by the same airline. However, in other embodiments, each valve has its own air line.Ganging the valves as shown in the exemplary embodiment creates thefluid-flow described above. In some embodiments, ganging the valves alsoensures the appropriate valves are opened and closed to dictate thefluid pathways as desired.

In the exemplary embodiment, the fluid valves are volcano valves, asdescribed in more detail in this specification. Although the fluidflow-path schematic has been described with respect to a particular flowpath, in various embodiments, the flow paths can change based on theactuation of the valves and the pumps. Additionally, the terms inlet andoutlet as well as first fluid and second fluid are used for descriptionpurposes only. In other embodiments, an inlet can be an outlet, as wellas, a first and second fluid may be different fluids or the same fluidtypes or composition.

Referring now to FIGS. 10A-10E, the top plate 1000 of the exemplaryembodiment of the cassette is shown. Referring first to FIGS. 10A and10B, the top view of the top plate 1000 is shown. In the exemplaryembodiment, the pod pumps 820, 828 and the balancing pods 812, 822 onthe top plate, are formed in a similar fashion. In the exemplaryembodiment, the pod pumps 820, 828 and balancing pods 812, 822, whenassembled with the bottom plate, have a total volume of capacity of 38ml. However, in various embodiments, the total volume capacity can begreater or less than in the exemplary embodiment. The first fluid inlet810 and the second fluid outlet 816 are shown.

Referring now to FIGS. 10C and 10D, the bottom view of the top plate1000 is shown. The fluid paths are shown in this view. These fluid pathscorrespond to the fluid paths shown in FIG. 9B in the midplate 900. Thetop plate 1000 and the top of the midplate form the liquid or fluid sideof the cassette for the pod pumps 820, 828 and for one side of thebalancing pods 812, 822. Thus, most of the liquid flow paths are on thetop and midplates. The other side of the balancing pods' 812, 822 flowpaths is located on the inner side of the bottom plate, not shown here,shown in FIGS. 11A-11B.

Still referring to FIGS. 10C and 10D, the pod pumps 820, 828 andbalancing pods 812, 822 include a groove 1002. The groove 1002 is shownhaving a particular shape, however, in other embodiments, the shape ofthe groove 1002 can be any shape desirable. The shape shown in FIGS. 10Cand 10D is the exemplary embodiment. In all embodiments of the groove1002, the groove forms a path between the fluid inlet side and the fluidoutlet side of the pod pumps 820, 828 and balancing pods 812, 822.

The groove 1002 provides a fluid path whereby when the membrane is atthe end of stroke, there is still a fluid path between the inlet andoutlet such that the pockets of fluid or air do not get trapped in thepod pump or balancing pod. The groove 1002 is included in both theliquid and air sides of the pod pumps 820, 828 and balancing pods 812,822 (see FIGS. 11A-11B with respect to the air side of the pod pumps820, 828 and the opposite side of the balancing pods 812, 822).

The liquid side of the pod pumps 820, 828 and balancing pods 812, 822,in the exemplary embodiment, include a feature whereby the inlet andoutlet flow paths are continuous while the outer ring 1004 is alsocontinuous. This feature allows for the seal, formed with the membrane(not shown) to be maintained.

Referring to FIG. 10E, the side view of the exemplary embodiment of thetop plate 1000 is shown. The continuous outer ring 1004 of the pod pumps820, 828 and balancing pods 812, 822 can be seen.

Referring now to FIGS. 11A-11E, the bottom plate 1100 is shown.Referring first to FIGS. 11A and 11B, the inside surface of the bottomplate 1100 is shown. The inside surface is the side that contacts thebottom surface of the midplate (not shown, see FIG. 9E). The bottomplate 1100 attaches to the air lines (not shown). The correspondingentrance holes for the air that actuates the pod pumps 820, 928 andvalves (not shown, see FIG. 9E) in the midplate can be seen 1106. Holes1108, 1110 correspond to the second fluid inlet and second fluid outletshown in FIG. 9G, 824, 826 respectively. The corresponding halves of thepod pumps 820, 828 and balancing pods 812, 822 are also shown, as arethe grooves 1112 for the fluid paths. Unlike the top plate, the bottomplate corresponding halves of the pod pumps 820, 828 and balancing pods812, 822 make apparent the difference between the pod pumps 820, 828 andbalancing pods 812, 822. The pod pumps 820, 828 include only a air pathon the second half in the bottom plate, while the balancing pods 812,822 have identical construction to the half in the top plate. Again, thebalancing pods 812, 822 balance liquid, thus, both sides of themembrane, not shown, will include a liquid fluid path, while the podpumps 820, 828 are pressure pumps that pump liquid, thus, one sideincludes a liquid fluid path and the other side, shown in the bottomplate 1100, includes an air actuation chamber or air fluid path.

In the exemplary embodiment of the cassette, sensor elements areincorporated into the cassette so as to discern various properties ofthe fluid being pumped. In one embodiment, the three sensor elements areincluded. In the exemplary embodiment, the sensor elements are locatedin the sensor cell 1114. The cell 1114 accommodates three sensorelements in the sensor element housings 1116, 1118, 1120. In theexemplary embodiment, two of the sensor housings 1116, 1118 accommodatea conductivity sensor element and the third sensor element housing 1120accommodates a temperature sensor element. The conductivity sensorelements and temperature sensor elements can be any conductivity ortemperature sensor elements in the art. In one embodiment, theconductivity sensor elements are graphite posts. In other embodiments,the conductivity sensor elements are posts made from stainless steel,titanium, platinum or any other metal coated to be corrosion resistantand still be electrically conductive. The conductivity sensor elementswill include an electrical lead that transmits the probe information toa controller or other device. In one embodiment, the temperature sensoris a thermister potted in a stainless steel probe. However, in alternateembodiments, a combination temperature and conductivity sensor elementsis used similar to the one described in co-pending U.S. PatentApplication entitled Sensor Apparatus Systems, Devices and Methods filedOct. 12, 2007 and published as Publication No. US 2008/0240929. In thisembodiment, the sensor cell 1114 is a single opening to the fluid lineor a single connection to the fluid line.

In alternate embodiments, there are either no sensors in the cassette oronly a temperature sensor, only one or more conductivity sensors or oneor more of another type of sensor.

Still referring to FIGS. 11A and 11B, the actuation side of the meteringpump 830 is also shown as well as the corresponding air entrance hole1106 for the air that actuates the pump.

Referring now to FIGS. 11C and 11D, the outer side of the bottom plate1100 is shown. The valve, pod pumps 820, 828 and metering pump 830 airline connection points 1122 are shown. Again, the balancing pods 812,822 do not have air line connection points as they are not actuated byair. As well, the corresponding openings in the bottom plate 1100 forthe second fluid outlet 824 and second fluid inlet 826 are shown.

Referring now to FIG. 11E, a side view of the bottom plate 1100 isshown. In the side view, the rim 1124 that surrounds the inner bottomplate 1100 can be seen. The rim 1124 is raised and continuous, providingfor a connect point for the membrane (not shown). The membrane rests onthis continuous and raised rim 1124 providing for a seal between thehalf of the pod pumps 820, 828 and balancing pods 812, 822 in the bottomplate 1100 and the half of the pod pumps 820, 828 and balancing pods812, 822 in the top plate (not shown, see FIGS. 10A-10D).

5.1 Membranes

In the exemplary embodiment, the membrane is a double o-ring membrane asshown in FIG. 6A. However, in some embodiments, a double o-ring membranehaving texture, including, but not limited to, the various embodimentsin FIGS. 6B-6F may be used.

Referring now to FIGS. 12A and 12B, the assembled exemplary embodimentof the cassette 1200 is shown. FIGS. 12C and 12D are exploded views ofthe exemplary embodiment of the cassette 1200. The membranes 1210 areshown. As can be seen from FIGS. 12C and 12D, there is one membrane 1220for each of the pods pumps and balancing pods. In the exemplaryembodiment, the membrane for the pod pumps and the balancing pods areidentical. The membrane in the exemplary embodiment is a double o-ringmembrane as shown in FIGS. 6A-6B. However, in alternate embodiments, anydouble o-ring membrane may be used, including, but not limited to, thevarious embodiments shown in FIGS. 6C-6F. However, in other embodiments,the double o-ring membrane is used in the balancing pods, but a singleo-ring membrane, as shown in FIGS. 4A-4D is used in the pod pumps.

The membrane used in the metering pump 1224, in the preferredembodiment, is shown in more detail in FIG.5G, with alternateembodiments shown in FIGS. 5E, 5F and 5H. The membrane used in thevalves 1222 is shown in more detail in FIG. 2E, with alternateembodiments shown in FIGS. 2F-2G. However, in alternate embodiments, themetering pump membrane as well as the valve membranes may containtextures, for example, but not limited to, the textures shown on the podpump/ balancing pod membranes shown in FIGS. 5A-5D.

One embodiment of the conductivity sensor elements 1214, 1216 and thetemperature sensor 1218, which make up the sensor cell 1212, are alsoshown in FIGS. 12C and 12D. Still referring to FIGS. 12C and 12D, thesensor cell housing 1414 includes areas on the bottom plate 1100 and themidplate 900. O-rings seal the sensor housing 1414 from the fluid lineslocated on the upper side of the midplate 900 shown in FIG. 12C and theinner side of the top plate 1000 shown in FIG. 12D. However, in otherembodiments, an o-ring is molded into the sensor cell, or any othermethod of sealing can be used.

5.2 Cross Sectional Views

Referring now to FIGS. 13A-13C, various cross sectional views of theassembled cassette are shown. Referring first to FIG. 13A, the membrane1220 is shown in a balancing pod 812 and a pod pump 828. As can be seenfrom the cross section, the double o-ring of the membrane 1220 issandwiched by the midplate 900, the bottom plate 1100 and the top plate1000.

Referring now to FIG. 13B, the two conductivity sensor elements 1214,1216 and the temperature sensor element 1218 are shown. As can be seenfrom the cross section, the sensor elements 1214, 1216, 1218 are in thefluid line 1302. Thus, the sensor elements 1214, 1216, 1218 are in fluidconnection with the fluid line and can determine sensor data of thefirst fluid entering the first fluid inlet 810. Referring now to FIG.13C, this cross sectional view shows the metering pump 830 as well asthe structure of the valves.

As described above, the exemplary embodiment is one cassette embodimentthat incorporates the exemplary fluid flow-path schematic shown in FIG.8A. However, there are alternate embodiments of the cassette thatincorporate many of the same features of the exemplary embodiment, butin a different structural design. Additionally, there are alternateembodiment fluid flow paths, for example, the fluid flow path schematicshown in FIG. 8B. The alternate embodiment cassette structurecorresponding to this schematic is shown in FIGS. 14A-18.

Referring now to FIGS. 14A-14E, views of an alternate embodiment of thetop plate 1400 are shown. The features of the top plate 1400 arealternate embodiments of corresponding features in the exemplaryembodiment.

Referring now to FIGS. 15A-15E, views of an alternate embodiment of themidplate 1500 are shown. FIGS. 16A-16E show views of an alternateembodiment of the bottom plate 1600.

Referring now to FIGS. 17A-17B, an assembled alternate embodiment of thecassette 1700 is shown. FIGS. 17C-17D show exploded views of thecassette 1700. FIG. 17E is a cross sectional view of the assembledcassette 1700.

Referring now to FIGS. 18A-22B, another alternate embodiment of thecassette is shown. In this embodiment, when the cassette is assembled,as shown in FIGS. 21A-21B, the plates 1800, 1900, 2000 are sealed fromeach other using gaskets. Referring to FIGS. 21C-21D, the gaskets 2110,2112 are shown. This embodiment additionally includes membranes (notshown). FIG. 22A is a cross sectional view of the assembled cassette,the gaskets 2110, 2112 relation to the assembled cassette assembly isshown.

5.3 Exemplary Embodiments of the Pumping Cassette

The pumping cassette can be used in a myriad of applications. However,in one exemplary embodiment, the pumping cassette is used to balancefluid going into the first fluid inlet and out the first fluid outletwith fluid coming into the cassette through the second fluid inlet andexiting the cassette through the second fluid outlet (or vice versa).The pumping cassette additionally provides a metering pump to remove avolume of fluid prior to that volume affecting the balancing pods oradds a volume of fluid prior to the fluid affecting the balancing pods.

The pumping cassette may be used in applications where it is criticalthat two fluid volumes are balanced. Also, the pumping cassette impartsthe extra functionality of metering or bypassing a fluid out of thefluid path, or adding a volume of the same fluid or a different fluidinto the fluid path. The flow paths shown in the schematic arebi-directional, and various flow paths may be created by changing thevalve locations and or controls, or adding or removing valves.Additionally, more metering pumps, pod pumps and/or balancing pods maybe added, as well as, more or less fluid paths and valves. Additionally,inlets and outlets may be added as well, or the number of inlets oroutlets may be reduced.

One example is using the pumping cassette as an inner dialysate cassetteas part of a hemodialysis system. Clean dialysate would enter thecassette through the first fluid inlet and pass through the sensorelements, checking if the dialysate is at the correct concentrationand/or temperature. This dialysate would pass through the balancing podsand be pumped through the first fluid outlet and into a dialyzer. Thesecond fluid in this case is used or impure dialysate from the dialyzer.This second fluid would enter through the second fluid inlet and balancewith the clean dialysate, such that the amount of dialysate that goesinto the dialyzer is equal to the amount that comes out.

The metering pump may be used to remove additional used dialysate priorto that volume being accounted for in a balancing pod, thus, creating a“false” balancing chamber through an ultra filtration (“UF”) bypass. Thesituation is created where less clean dialysate by a volume equaled tothe bypassed volume will enter the dialyzer.

In this embodiment, the valves controlling fluid connections to thebalancing chambers shall be oriented such that the volcano feature ofthe valve is on the fluid port connected to the balancing chamber. Thisorientation directs most of the fluid displaced by the valve as it isthrown away from the balancing chamber.

The valves controlling fluid connections to the UF pump shall beoriented such that the volcano feature of the valve is on the fluid portconnected to the pumping chamber. In the exemplary embodiment, thenominal stroke volume of each inside dialysate pump chamber shall be 38ml. The nominal volume of each balancing pod shall be 38 ml. The strokevolume of the UF pump shall be 1.2 ml+/−0.05 ml. The inner dialysatepump low-pressure pneumatic variable valves shall vent to ambientatmospheric pressure. This architecture feature minimizes the chancethat dissolved gas will leave the dialysate while inside of thebalancing chambers. Other volumes of pod pumps, balancing chambers andmetering pumps are easily discernable and would vary depending on theapplication. Additionally, although the embodiment described discussesventing to ambient, in other applications, negative pressure can beadministered.

In various embodiments of the cassette, the valve architecture varies inorder to alter the fluid flow path. Additionally, the sizes of the podpumps, metering pump and balancing pods may also vary, as well as thenumber of valves, pod pumps, metering pumps and balancing pods. Althoughin this embodiment, the valves are volcano valves, in other embodiments,the valves are not volcano valves and in some embodiments are smoothsurface valves.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the exemplary embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention.

What is claimed is:
 1. (canceled)
 2. A fluid-balancing cassettecomprising: a first and a second fluid-balancing pod, each chamber podhaving a first port separated from an opposing second port by a flexiblemembrane, the flexible membrane dividing the fluid-balancing pod intovariable volume first and second chambers, wherein a total fluid volumeof the fluid-balancing chamber pod is a sum of the volumes of the firstand second chambers; a first and a second diaphragm pump, an outlet ofthe first diaphragm pump having a valved connection to the second portof the first fluid-balancing pod and an outlet of the second diaphragmpump having a valved connection to the second port of the secondfluid-balancing pod, wherein a full stroke volume of each diaphragm pumpmatches the total fluid volume of the fluid-balancing pod to which it isconnected; a first fluid flowpath connecting a first inlet of thecassette to a first outlet of the cassette, wherein the first fluidflowpath has separate valved connections to the first port of the firstfluid-balancing pod and to the first port of the second fluid-balancingpod; and a second fluid flowpath connecting a second inlet of thecassette to a second outlet of the cassette, wherein the second fluidflowpath has separate valved connections to an inlet of the firstdiaphragm pump and to an inlet of the second diaphragm pump, wherein thefluid-balancing cassette is configured to allow the full stroke volumeof the first or the second diaphragm pump, which contains a second fluidreceived from the second inlet to displace a substantially equal volumeof a first fluid contained within the first or second fluid-balancingpod, the first fluid having previously been received by the first orsecond fluid-balancing pod from the first inlet.
 3. The fluid-balancingcassette of claim 2, further comprising a third diaphragm pump having avalved connection to a third fluid flowpath that connects the secondinlet to the second outlet, bypassing the first and secondfluid-balancing pods.
 4. The fluid-balancing cassette of claim 2,wherein the first fluid flowpath comprises a sensor cell located betweenthe first fluid inlet and the first port, respectively, of the first andsecond fluid-balancing pods.
 5. The fluid-balancing cassette of claim 4,wherein the sensor cell comprises two or three sensor element housingsconfigured to mate with temperature or conductivity probes to detecttemperature or conductivity of the first fluid.
 6. The fluid-balancingcassette of claim 2, wherein the first fluid flowpath comprises a firstbranch connected to the first port of the first fluid-balancing pod anda second branch connected to the first port of the secondfluid-balancing pod, each said branch comprising a first branch valveconfigured to direct an incoming first fluid to the first or secondfluid-balancing pod.
 7. The fluid-balancing cassette of claim 6, whereineach said branch comprises a second branch valve downstream of each ofthe first ports of the first and second fluid-balancing pods,respectively, wherein the fluid-balancing cassette is configured forfilling each fluid-balancing pod with the first fluid through operationof the first and second branch valves.
 8. The fluid-balancing cassetteof claim 2, wherein the second fluid flowpath comprises a first branchconnected to the inlet of the first diaphragm pump and a second branchconnected to the inlet of the second diaphragm pump, each said branchcomprising a pump inlet valve upstream of each diaphragm pump, a pumpoutlet valve located between each diaphragm pump and the second port ofeach of the fluid-balancing pods, and a branch outlet valve downstreamof the second port of each of the fluid-balancing pods, wherein thefluid-balancing cassette is configured for filling each fluid-balancingpod with the second fluid through operation of the pump inlet valves,the pump outlet valves, and the branch outlet valves.
 9. Afluid-balancing cassette comprising: a first and a secondfluid-balancing pod, each pod having a first port separated from anopposing second port by a flexible membrane, the flexible membranedividing the fluid-balancing pod into variable volume first and secondchambers, wherein a total fluid volume of the fluid-balancing pod is asum of the volumes of the first and second chambers; a first and asecond diaphragm pump, an outlet of the first diaphragm pump having avalved connection to the second port of the first fluid-balancing podand an outlet of the second diaphragm pump having a valved connection tothe second port of the second fluid-balancing pod, wherein a full strokevolume of each diaphragm pump matches the total fluid volume of thefluid-balancing pod to which it is connected; a first fluid flowpathconnecting a first inlet of the cassette to a first outlet of thecassette, wherein the first fluid flowpath has separate valvedconnections to the first port of the first fluid-balancing pod and tothe first port of the second fluid-balancing pod; a second fluidflowpath connecting a second inlet of the cassette to a second outlet ofthe cassette, wherein the second fluid flowpath has separate valvedconnections to an inlet of the first diaphragm pump and to an inlet ofthe second diaphragm pump; and a third fluid flowpath comprising a thirddiaphragm pump, having a valved connection to the second inlet andsecond outlet of the cassette, and bypassing the first and secondfluid-balancing pods, wherein the fluid-balancing cassette is configuredto allow the full stroke volume of the first or the second diaphragmpump, which contains a second fluid received from the second inlet todisplace a substantially equal volume of a first fluid contained withinthe first or second fluid-balancing pod, the first fluid havingpreviously been received by the first or second fluid-balancing pod fromthe first inlet.
 10. The fluid-balancing cassette of claim 9, whereinthe first fluid flowpath comprises a sensor cell located between thefirst fluid inlet and the first port, respectively, of the first andsecond fluid-balancing pods.
 11. The fluid-balancing cassette of claim10, wherein the sensor cell comprises two or three sensor elementhousings configured to mate with temperature or conductivity probes todetect temperature or conductivity of the first fluid.
 12. Thefluid-balancing cassette of claim 9, wherein the first fluid flowpathcomprises a first branch connected to the first port of the firstfluid-balancing pod and a second branch connected to the first port ofthe second fluid-balancing pod, each said branch comprising a firstbranch valve configured to direct an incoming first fluid to the firstor second fluid-balancing pod.
 13. The fluid-balancing cassette of claim12, wherein each said branch comprises a second branch valve downstreamof each of the first ports of the first and second fluid-balancing pods,respectively, wherein the fluid-balancing cassette is configured forfilling each fluid-balancing pod with the first fluid through operationof the first and second branch valves.
 14. The fluid-balancing cassetteof claim 9, wherein the second fluid flowpath comprises a first branchconnected to the inlet of the first diaphragm pump and a second branchconnected to the inlet of the second diaphragm pump, each said branchcomprising a pump inlet valve upstream of each diaphragm pump, a pumpoutlet valve located between each diaphragm pump and the second port ofeach of the fluid-balancing pods, and a branch outlet valve downstreamof the second port of each of the fluid-balancing pods, wherein thefluid-balancing cassette is configured for filling each fluid-balancingpod with the second fluid through operation of the pump inlet valves,the pump outlet valves, and the branch outlet valves.
 15. Afluid-balancing cassette comprising: a first and a secondfluid-balancing pod, each pod having a first port separated from anopposing second port by a flexible membrane, the flexible membranedividing the fluid-balancing pod into variable volume first and secondchambers, wherein a total fluid volume of the fluid-balancing pod is asum of the volumes of the first and second chambers; a first and asecond diaphragm pump, an outlet of the first diaphragm pump having avalved connection to the second port of the first fluid-balancing podand an outlet of the second diaphragm pump having a valved connection tothe second port of the second fluid-balancing pod, wherein a full strokevolume of each diaphragm pump matches the total fluid volume of thefluid-balancing pod to which it is connected; a first fluid flowpathconnecting a first inlet of the cassette to a first outlet of thecassette, wherein the first fluid flowpath has separate valvedconnections to the first port of the first fluid-balancing pod and tothe first port of the second fluid-balancing pod, and wherein the firstfluid flowpath comprises a sensor cell located between the first fluidinlet and the first port, respectively, of the first and secondfluid-balancing pods; and a second fluid flowpath connecting a secondinlet of the cassette to a second outlet of the cassette, wherein thesecond fluid flowpath has separate valved connections to an inlet of thefirst diaphragm pump and to an inlet of the second diaphragm pump,wherein the fluid-balancing cassette is configured to allow the fullstroke volume of the first or the second diaphragm pump, which containsa second fluid received from the second inlet to displace asubstantially equal volume of a first fluid contained within the firstor second fluid-balancing pod, the first fluid having previously beenreceived by the first or second fluid-balancing pod from the firstinlet.
 16. The fluid-balancing cassette of claim 15, further comprisinga third diaphragm pump having a valved connection to a third fluidflowpath that connects the second inlet to the second outlet, bypassingthe first and second fluid-balancing pods.
 17. The fluid-balancingcassette of claim 15, wherein the sensor cell comprises two or threesensor element housings configured to mate with temperature orconductivity probes to detect temperature or conductivity of the firstfluid.
 18. The fluid-balancing cassette of claim 15, wherein the firstfluid flowpath comprises a first branch connected to the first port ofthe first fluid-balancing pod and a second branch connected to the firstport of the second fluid-balancing pod, each said branch comprising afirst branch valve configured to direct an incoming first fluid to thefirst or second fluid-balancing pod.
 19. The fluid-balancing cassette ofclaim 18, wherein each said branch comprises a second branch valvedownstream of each of the first ports of the first and secondfluid-balancing pods, respectively, wherein the fluid-balancing cassetteis configured for filling each fluid-balancing pod with the first fluidthrough operation of the first and second branch valves.
 20. Thefluid-balancing cassette of claim 15, wherein the second fluid flowpathcomprises a first branch connected to the inlet of the first diaphragmpump and a second branch connected to the inlet of the second diaphragmpump, each said branch comprising a pump inlet valve upstream of eachdiaphragm pump, a pump outlet valve located between each diaphragm pumpand the second port of each of the fluid-balancing pods, and a branchoutlet valve downstream of the second port of each of thefluid-balancing pods, wherein the fluid-balancing cassette is configuredfor filling each fluid-balancing pod with the second fluid throughoperation of the pump inlet valves, the pump outlet valves, and thebranch outlet valves.